The present invention relates to a stirring apparatus for agitating and mixing solutions by a batch treatment. More particularly, the present invention relates to improvements for enhancing the treatment speed in an agitating and mixing treatment and also enhancing the treatment quality at the same time.
For example, a photographic silver halide emulsion, which is used as a photosensitive material, is made by agitating and mixing solutions in a batch treatment. This photographic emulsion of silver halide is formed when a water-soluble silver salt solution and a water-soluble halide solution, which are addition solutions, are added to a colloidal aqueous solution, which is a primary component solution, and the solutions are agitated and mixed with each other.
However, when the concentration of each addition solution is high in the agitating and mixing process, grains of silver halide formed in the process grow excessively and large grains are formed. When silver halide grains formed in the reaction of the addition solutions stay in the solution, uniform aging of the grains of silver halide is obstructed, and further it becomes impossible to form a photographic silver halide emulsion of uniform quality.
That is, the following are important in the stirring apparatus used for the formation of a photographic silver halide emulsion. The addition solution is instantaneously diluted, agitated and mixed, so that silver halide grains of small size can be formed. In order to uniformly, quickly disperse and ripen the thus formed silver halide grains in a colloidal aqueous solution which is a primary component solution, it is necessary to facilitate the circulation of the primary component solution.
In order to solve the above problems, the stirring apparatus shown in FIGS. 6 and 7 was proposed.
This stirring apparatus 1 was disclosed in the U.S. Pat. No. 4,289,733 which corresponds to the Examined Japanese Patent Publication No. Sho 55-10545 applied by the present applicant, which includes: a reaction vessel 4 for storing a colloidal aqueous solution 2 which is a primary component solution when a photographic emulsion of silver halide is produced; a mixing device 6, formed into a cylindrical shape, both ends of which are open, the mixing device 6 being arranged in the reaction vessel 4 so that it can be dipped in the colloidal aqueous solution 2; conduits 10, 11 for supplying a water-soluble silver salt solution and a water-soluble halide solution into the mixing device 6 from one opening 8 of the mixing device 6; and two agitator blades consisting of a lower agitator blade 13 and an upper agitator blade 17 which are rotated in the mixing device 6.
The mixing device 6 is arranged being dipped in the colloidal aqueous solution 2 in such a manner that openings of both ends of the mixing device 6 are set in the horizontal direction.
The lower agitator blade 13 is a paddle impeller and arranged at a position close to the lower end opening 8 of the mixing device 6 as shown in FIG. 7. When the lower agitator blade 13 is rotated round the central axis of the mixing device 6, a radial flow is formed which mainly flows in the circumferential and the radial direction of the mixing device 6, so that the solutions in the mixing device 6 can be agitated and mixed. Therefore, the addition solution is instantaneously diluted and then agitated and mixed. Due to the foregoing, silver halide grains of small grain size can be formed in the mixing device 6.
On the other hand, the upper agitator blade 17 is a jet impeller and arranged at a position close to the upper end opening 15 of the mixing device 6 as shown in FIG. 7. When the upper agitator blade 17 is rotated round the central axis of the mixing device 6, an axial flow is formed which flows along the axis of the mixing device 6 from the lower end opening 8 to the upper end opening 15 of the mixing device 6. The upper agitator blade 17 discharges the solution, which is agitated and mixed by the lower agitator blade 13, from the upper end opening 15 of the mixing device 6 to the outside of the mixing device 6. At the same time, the upper agitator blade 17 sucks the colloidal aqueous solution 2 from the outside of the mixing device 6 into the mixing device 6 via the lower end opening 8.
That is, the upper agitator blade 17 facilitates the circulation of the colloidal aqueous solution 2 in the reaction vessel 4 so that the silver halide grains formed by the lower agitator blade 13 can be quickly, uniformly dispersed and ripened in the colloidal aqueous solution (bulk liquid) 2 in the reaction vessel 4.
The lower agitator blade 13 and the upper agitator blade 17 are fixed to the same rotary shaft 19. The rotary shaft 19 is rotated by a motor 21 arranged on the cover 20 of the reaction vessel 4.
In this connection, the conduits 10, 11 supply the addition solutions into the opening 8 via supply holes 25, 26 arranged on the bottom wall 23 of the mixing device which forms the lower end opening 8 of the mixing device 6.
However, the following problems may be encountered when the above conventional stirring apparatus 1 is operated. The radial flow formed by the lower agitator blade 13 rotates the axial flow formed by the upper agitator blade 17 in the same direction. Therefore, vortexes are generated in the mixing device 6 and the reaction vessel 4, and air is involved in the vortexes and foam is made in the process of agitation. Therefore, it is impossible to circulate the colloidal aqueous solution 2 in the reaction vessel as desired. As a result, the silver halide grains can not be sufficiently dispersed and ripened in the bulk solution. Accordingly, there is a possibility that the treatment speed and the quality of treatment are deteriorated.